1. Technical Field of the Invention
The present invention relates to a network relay apparatus which relays data between a plurality of communication networks.
2. Related Art
A network relay apparatus has a plurality of input/output ports each of which is connected to each of a plurality of communication networks (hereinafter referred to just as “networks”) so as to enable communication therebetween. In this apparatus, when a data is relayed from one network to another network, the data is inputted from an input port connected to the former network, and an output port connected to the latter network is decided based on additional information on the input data, so that the data is outputted from the decided output port. The “additional information” herein refers, for example, to such information that indicates the type of data and an addressee of the data, i.e. information on anything other than the data body.
In order to improve reliability in relaying data in the network relay apparatuses which are arranged as mentioned above, various techniques have been suggested lately. For example, Japanese Published Unexamined Application No. 2000-244548 suggests a technique in which a buffer is provided for each of the types of data to be relayed to prevent vanishment of data when the data is relayed.
However, in the above network relay apparatuses, depending on a fault that has occurred in the apparatus, input data tends not to be outputted from a correct output port from which the data should have been originally outputted. The reliability of the above apparatuses therefore cannot be sufficiently high.
For example, in a network relay apparatus, a data table is generally referenced in deciding an output port from which the data inputted from an input port should be outputted, the data table cataloging correspondences between pieces of additional information on the data and output ports. Under such circumstances, if a fault occurs by which the catalog contents of the data table are vanished or rewritten for some reason, the correspondences between the additional information and the output ports may turn out to be wrong, or rather no suitable correspondences may turn out to exist in the data table.
In this case, if an output port data corresponding to the additional information on the data inputted from an input port has been deleted from the data table, the data will no longer be outputted. Also, if the output port data corresponding to the additional information has been rewritten, the data will not be outputted from a correct output port from which the data should have been originally outputted.
In view of the above, it is desirable to provide an arrangement for a network relay apparatus, which is capable of detecting occurrences of such faults. An example of an arrangement for detecting occurrences of such faults may be one that provides a process which is dedicated to detect such faults by, for example, continuously or periodically checking contents of an incorporated memory or operational conditions of hardware. However, such an arrangement may not be realistic from a viewpoint of processing load or processing time required for checking.